This invention relates to fire sensing in an earlier stage and yet with minimum error.
As known well, fire expands through following stages:
1. Incipient stage: Incipient and invisible combustion stage and may be said to be not fire but a pre-combustion stage. This stage can be sensed only by a high sensitivity combustion sensor such as an N type semiconductor reducing gas sensor or chemical sensor.
2. Smoldering stage: Combustion stage products are now apparent as smoke. Flame and heat are not yet developed.
3. Flame stage: Flame begins to appear with slight heating effect.
4. Heat stage: High heat is dissipated uncontrollably.
A fire is developed generally through these stages, although the stage duration may differ depending on the respective fire condition. The above respective stages provide their own characteristics and symptoms, and accordingly need different sensors peculiar to the respective stage.
Therefore, if we can detect the stage symptoms separately, we can confirm the fire perfectly by the main symptom as compared with the preceding stage symptom. This is the fundamental idea of this invention for accurately detecting fire in its early stage.
However, simply compounding different symptom sensors such as in "logical AND or OR" can only serve to exclude fire sensing error and has no advantage other than fire sensing error prevention, which can be attained simply by sensing a fire in its developed stage or with a low sensitivity fire sensor. In sensing fire exposing human life to serious danger, there is always another objective; that is, sensing a fire in its earlier stage. The object of this invention is attaining of these two essential objectives, earlier sensing and yet freedom from error.
In this invention, freedom from error is attained by super-imposition of different fire stage sensor outputs and earlier sensing is acomplished in that when an earlier fire stage sensor detects fire, its output is coupled to the subsequent later fire stage sensor so as to raise the latter sensor's sensitivity which is arranged in the latter to be controllable, and accordingly the compounding of different fire stage sensors in this invention attains simultaneously two conditions in fire sensing, "quick and error free".
On the contrary, the conventional prior fire sensor compounding aims principally to exclude sensing error only lacking provision for early sensing.
In addition, the objects of the conventional compounding of different sensors such as available ionization smoke detector and grid resistance compounding are to compensate or cover defects peculiar to individual sensor itself and exclude errors due to these defects. For example, the ionization smoke sensor detects fire by sensing relatively large particles of carbonous substances, but can not sense contaminate, or conductive or wet molecules, while the grid resistance can detect the latter nuisance but can not sense large carbonous particles. Therefore compounding of these two sensors excludes sensing error of fires by sensing concurrence of the above two symptoms that is, the purpose of this type is prevention of error only, unlike this invention.
Further, in general a sensor capable of detecting the weakest symptom or in other words, the earliest symptom of a fire can be said to be most sensitive. In fire sensing, a fire is developed continuously from incipient combustion to ultimate violent disaster and since no definite border can be clearly discriminated physically except that a fire is defined as an uncontrollable combustion and a combustion is not necessarily combined with a fire, earlier fire sensing is always related to fire sensing errors and sensitivity in fire sensing always conflicts with accuracy in sensing.
In this age of utmost respect for human life since a fire exposes many human lives to serious danger, quickness in sensing must be considered more important than errorlessness; in other words, priority must be placed on sensitivity instead of accuracy. Thus the object of this invention is to detect a fire as soon as possible with minimum errors.
Though the above statement is considered to be true, freedom from error also must not be neglected, since annoyance due to too frequent errors makes inevitable the cutting of power to the sensor and leads to disaster and the betrayal of the human relief sought by the fire sensor installation.
This invention also achieves the object of minimizing error by superimposing signals from different fire stage symptoms or final later fire stage sensing preceded by repeated checking of an earlier fire stage sensor as described previously.